Offshore drilling method and apparatus



May 19, 1970 Filed March 14, 1968 J. M. KELLNER 3,512,592

OFFSHORE DRILLING METHOD AND APPARATUS Q 2. Sheets-Sheet 1 FIG. 2

JACKSON M. KELLNER INVENTOR.

A TTORNEY May 19, 1970 I J. M. KELLNER 3,512,592

OFFSHORE DRILLING METHOD AND APPARATUS I 7 Filed March 14, 1968 2 Sheets-Sheet 2 [I M A 65 i I I\ i5 1 /////7 74- 71- i 77- r i 1/ I I e?- 1// 73/ f i I l E I .i U M/ a] I J J! il FIG. 4

JACKSON M. KELLNER INVENTOR.

ATTORNEY United States Patent 3 512 592 OFFSHORE DRrLLiNGMEmoD AND APPARATUS Jackson M. Kellner, Houston, Tex., assignor to Esso Production Research Company, a corporation of Dela- WBIE Filed Mar. 14, 1968, Ser. No. 712,973 Int. (:1. E21b 7/12; E21c 9/00 US. Cl. 1755 6 Claims ABSTRACT OF THE DISCLOSURE A method for coring unconsolidated subsurface formations from a floating drilling vessel wherein the upper portion of the drill string moves in response to vertical motion of the vessel and the lower portion is held in a fixed vertical position as the string is rotated. The apparatus employed generally includes a drill string containing an anchor member which permits rotation of the drill string but prevents vertical movement of the string below it, a slip joint in the drill pipe above the anchor member, and a rubber sleeve core barrel or similar device attached to the lower end of the drill string.

BACKGROUND OF THE INVENTION Field of the invention This invention pertains to the drilling of boreholes in the earth at offshore locations and is particularly concerned with the use of a rubber sleeve core barrel or similar apparatus for coring unconsolidated subsurface formations from a floating drilling vessel.

Description of the prior art It is often desirable to obtain samples of subterranean formations to determine their permeability, porosity, oil content, and other information. Methods for obtaining such samples are well known in the petroleum industry. Such methods generally involve the use of coring apparatus designed to cut cylindrical cores from the reservoir rock and encase them in a core barrel mounted near the lower end of a drill string. Such apparatus is very effective in consolidated formations in both onshore and offshore operations. Some formations, however, are unconsolidated and are therefore difficult to core with the equipment normally used in fully consolidated zones. The most effective way of obtaining core samples from these unconsolidated formations is to use a rubber sleeve core barrel. This coring apparatus cuts a cylindrical core from the unconsolidated formations and encases it within a long cylindrical rubber sleeve which supports the unconsolidated material and keeps it from disintegrating. Although the rubber sleeve barrel is very effective for onshore applications, certain features of the apparatus have made its use from floating vessels impracticable.

The rubber sleeve core barrel is a telescoping tool that utilizes hydraulic pressure to force a coring bit and lower core barrel section downwardly relative to a rubber sleeve and other components fastened to the lower end of the drill string. This use of hydraulic pressure is desirable because it permits the application of a constant force to the coring bit as it rotates at the bottom of the borehole. It requires that the drill string and the upper end of the rubber sleeve core barrel remain at the same elevation throughout the stroke of the core barrel. If the string moves downwardly, it will close the telescoping section of the barrel, thus rumpling the rub-ber sleeve and ruining the core. In onshore applications the drill string is locked in the rotary table to prevent such downward movement. Where the well is drilled from a floating drilling vessel, however, the drill string moves in response to vertical movement of the ship caused by wind, waves, currents, and

ice

the like. This vertical motion is normally compensated for by means of slip joints or similar devices within the drill string. The slip joints telescope to allow the upper portion of the drill string above them to move vertically relative to the lower portion of the string below them. This alleviates problems created by motion of the ship during ordinary drilling operations but creates new problems with respect to coring operations. Since the portion of the drill pipe below the slip joint is free to move downwardly, it tends to close the rubber sleeve core barrel and thus make its proper operation virtually impossible. A need therefore exists for a method and apparatus that will permit the coring of an unconsolidated formation with a rubber sleeve core barrel from a floating drilling vessel.

SUMMARY OF THE INVENTION The method and apparatus of this invention facilitate the coring of unconsolidated subsurface formations from floating drilling vessels with rubber sleeve core barrels or similar devices. The method involves the anchoring of the drill string at a point between the drilling vessel and the bottom of the borehole while permitting rotation of the entire string and vertical motion of the upper section above the anchor point relative to the lower section. In this fashion, while the upper section of the string remains free to elongate and contract to compensate for motion of the ship, the bottom section will continue to rotate at the same elevation, thus permitting coring operations with the rubber sleeve core barrel or other operations requiring the drill string to rotate at a fixed elevation.

Apparatus suitable for performing coring operations with a rubber sleeve core barrel in accordance with the invention includes a drill string having an upper and a lower section, means such as a slip joint or flexible high-pressure tubing between the upper and lower sections for permitting vertical movement of the upper section relative to the lower section, and a hydraulic drill string anchor, a marine swivel, or similar means mounted within the lower section of the drill string for anchoring the lower section to the borehole wall while permitting its rotation.

The method and apparatus of the invention permit coring operations to be successfully conducted from a floating drilling vessel with a rubber sleeve core barrel or any similarly operable device and therefore offer distinct advantages over systems used in the past.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic of the apparatus of the invention as assembled for coring a subsurface formation from a floating drilling vessel. FIG. 2 is an elevation, partly in cross-section, of a hydraulic drill string anchor suitable for use with the apparatus of FIG. 1. FIG. 3 schematically depicts an alternate configuration of the apparatus of the invention employing a marine swivel. FIG. 4 is an elevation, partly in cross-section, of an improved marine swivel suitable for use with the apparatus of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus shown in FIG. 1 includes a floating drilling vessel 11 held in place by lines extending to the ocean bottom '13. The surface of the water is indicated by reference numeral 15. Suspended from the drilling vessel is a string of drill pipe 17, which is protected from the ocean by a marine riser 19 extending between the vessel and a submerged wellhead 21. Within the borehole 23 beneath the wellhead is the continuation of the string of drill pipe shown containing a slip joint 25. A hydraulic anchor 27 having anchor shoes 29 for anchoring the drill string to the walls of the borehole is mounted in the drill string below the slip joint. Although the hydraulic anchor is depicted in FIG. 1 as anchoring the drill string to a string of surface casing 31, it could also be used to anchor the drill string to the walls of the borehole. A rubber sleeve core barrel assembly 33 is mounted at the bottom of the lower section of the drill string below hydraulic anchor 27. A coring bit 35 is connected to the lower end of the core barrel assembly. Rubber sleeve core barrels are commercially available from Christensen Diamond Products of Salt Lake City, Utah, and are described in volume 1 of the 196-67 Composite Catalog of Oil Feld Equipment and Services, published by the Gulf Publishing Company, Houston, Tex., at page 1367. Slip joint 25 is commercially available from a number of manufacturers. Typical of the commercial devices is the bumper sub manufactured by the Baash-Ross Division of Joy Manufacturing Company of Houston, Tex., illustrated in volume 1 of the 166-67 Composite Catalog at page 435.

The hydraulic drill string anchor shown in detail in FIG. 2 includes a hollow inner tubular mandrel 37 that extends through the tool and has ports 39 through its walls. These ports permit drilling fluid to pass from the hollow interior of the mandrel into an annular interior passageway 40 formed between the mandrel and the interior of a surrounding anchor shoe housing 43. The fluid flows from the passageway through ports 41 into cylindrical hydraulic chambers 42 within the anchor shoe housing. Upper thrust bearings 45 and lower radial bearings 47 are mounted between the mandrel and the anchor shoe housing. A cylindrical shoulder 48 on mandrel 37 transfers the load carried by the mandrel to the anchor shoe housing by means of the thrust bearings. The housing itself is a substantially cylindrical assembly within which the mandrel is held but is free to rotate along the bearing surfaces. A plurality of anchor shoes 49 are mounted in external apertures 50 in the anchor shoe housing. These shoes are constructed of steel or similar material and have exterior teeth 51 to improve their ability to grip the walls of the borehole or of the surface casing. The shoes are biased in an inward position by springs 53 and are surrounded by packing material 55 where they meet the inner walls of hydraulic chambers 41 contained within the interior of the housing. The drilling fluid functions as a hydraulic fluid. Sealing members 57 and 59 surround the mandrel where it enters and emerges from the cylindrical anchor shoe assembly housing.

During operation of the assembly depicted in FIGS. 1 and 2, the apparatus is first made up in sections and run into the borehole until coring bit 35 reaches the bottom. Pressurized drilling fluid is then directed down drill pipe 17 causing the hydraulically actuated anchor shoes of the anchor assembly to extend and grip the surface casing, or the walls of the borehole if no casing has been installed, thereby anchoring the drill string in place. The hydraulic pressure also causes the hydraulic piston located in the rubber sleeve core barrel to force the bit against the bottom of borehole 23. The reaction force is directed up drill string 17 and is opposed by the weight of the string, which is in turn supported by anchor 27. The section of drill string above the anchor assembly may then be hoisted up one-half the stroke of the slip joint so that the slip joint will be in its middle position when the vessel is in the midpoint of its vertical heave. The hydraulic pressure within the drill string will cause upward and downward forces to be generated by the slip joint within the drill string if an unbalanced slip joint is used. The upward force must be balanced by the weight of the drill string located above slip joint 25. The opposing downward force will be applied to the walls of the borehole by hydraulic anchor 27. Similarly, any net opposing upward force generated by the rubber sleeve core barrel 33 will be transmitted up drill pipe 17 to hydraulic drill string anchor 27, where it will be applied to the walls of the borehole or the surface casing. Thus no unbalanced forces will exist within the system and the rubber sleeve core barrel will advance downwardly as it is rotated, cutting a core sample of the unconsolidated formation.

Other apparatus may be employed in lieu of that shown in FIGS. 1 and 2. of the drawing. One alternate system which has certain advantages involves the placement of a marine swivel 61 on wellhead 21 as a substitute for hydraulic drill string anchor 27. In this system, depicted in FIG. 3, drill pipe 17 again extends from the drilling vessel 11 through a riser 19 into the borehole. Slip joint 25 is mounted in the section of the drill string between the floating vessel and the marine swivel. The marine swivel, mounted on wellhead 21 by means of adapter 22, supports the lower section of the drill string beneath it and the rubber sleeve core barrel at a fixed elevation, while permitting their rotation. Such swivels are commercially available and are typified by those manufactured by A-1 Bit & Tool Company of Oklahoma City, Okla., illustrated in volume 1 of the 1966-67 Composite Catalog at page 121.

During operation, the apparatus of FIG. 3 functions in much the same manner as the apparatus of FIGS. 1 and 2. The slip joint, if an unbalanced device, exerts upward and downward hydraulic forces as does the rubber sleeve core barrel. Drill collars can again be mounted above the slip joint to the extent they are necessary to balance the upward hydraulic forces. The downward forces are imparted through the swivel and wellhead to the ocean bottom. The downward force exerted hydraulically by the rubber sleeve core barrel is again applied to the bottom of the borehole, while the upward force is applied to the drill string be tween the rubber sleeve core barrel and the marine swivel. It will be apparent that the weight of the drill string between the swivel and the rubber sleeve core barrel should exceed the hydraulic force generated by the rubber sleeve core barrel. It may therefore be necessary to mount drill collars in the drill string above the rubber sleeve core barrel to maintain the lower part of the string in tension.

Unlike the hydraulic drill string anchor, the marine swivel is mechanically seated within the wellhead and cannot be released and lowered each time the rubber sleeve core barrel completes a stroke. This presents an operational problem, since commercial rubber sleeve core barrels may require ten to twenty strokes to fill the core barrel. One solution is to withdraw the drill string after each stroke to a point just below the marine swivel and insert a short sub, indicated by reference numeral 63 in FIG. 3, to correct the length of the drill string beneath the swivel. Another approach which is generally preferable to this is to use the improved marine swivel depicted in FIG. 4. The marine swivel shown includes a hollow, substantially cylindrical outer mandrel 65 rotatably connected by means of radial bearings 67 and thrust bearings 69 to an outer housing 71. This housing is constructed to seat in wellhead 73 by means of adapter 74 and support the drill string. The load supported by the outer mandrel is transferred to the housing 71 by a cylindrical shoulder 72 on the outer mandrel which rests on thrust bearings 69. Sea]- ing members 81 and 83 surround the outer mandrel where it enters and emerges from the outer housing. An inner tubular mandrel 75 is slidably mounted within the outer mandrel and is fitted with hydraulically actuated wall anchors 77 that extend through apertures 78 in the walls of the inner mandrel. These wall anchors are sealably mounted in the apertures on the inner mandrel by means of resilient sealing elements 79. The anchors are normally retracted and extend outwardly in response to differential pressure between the inner mandrel and the annulus. After the rubber sleeve core barrel completes its stroke, the mud pressure is released and the wall anchors 77 are retracted from the interior walls of the outer mandrel. The inner mandrel is then lowered within the outer mandrel 65 a distance equivalent to the length of the stroke of the rubber sleeve core barrel so that coring can resume. The drilling fluid pressure is then increased, causing the wall anchor shoes to extend outwardly and grip the mandrel. Rotation of the drill pipe is resumed with the drill string supported within the mandrel sections rotating in relation to the outer housing.

An additional advantage of the marine swivel of FIG. 4 is in spacing out the drill string. With conventional apparatus it is necessary to lower the drill string until it touches bottom and then withdraw a sufiicient length of pipe form the hole to place the marine swivel in the string. Because the marine swivel mechanically seats within the wellhead, the length of the drill string below it should be exactly the length required to extend to the bottom for effective contact with the bottom of the hole. Motion of the ship makes this a diflicult and time-consuming undertaking and often several trials are required before the proper spacing is determined. With the marine swivel of FIG. 4, all that is necessary is to lower the drill string until it reaches bottom and then increase the pressure within the drill string so as to engage the hydraulic anchors. It can thus be seen that the improved marine swivel is much more efficient in spacing out operations than existing marine swivels.

Although the apparatus of the invention has been discussed primarily in terms of applications utilizing a rubber sleeve core barrel, it should be apparent that many other applications also exist. It will be useful in any circumstance where the upper end of a pipe string must be free to move vertical motion in the lower end of the drill pipe cannot be tolerated without jeopardizing the operation.

I claim:

1. A method for coring a subterranean formation with a hydraulically extensible rubber sleeve core barrel wherein a slip joint is mounted in the drill string which comprises anchoring the drill string at a point between the slip joint and the rubber sleeve core barrel, rotating the core barrel, and simultaneously applying sufficient hydraulic pressure to the interior of the drill string to extend the core barrel downwardly relative to the anchored portion of the drill string and into contact with the formation.

2. A method for coring a subsurface formation with a hydraulically extensible core barrel wherein the drill string includes a means to compensate for vertical motion of the vessel relative to the earth which comprises:

(a) anchoring the drill string at a point between the compensation means and the core barrel;

(b) rotating the core barrel; and

(c) simultaneously applying sufiicient hydraulic pressure to the interior of the drill string to extend the core barrel downwardly relative to the anchored portion of the drill string and into contact with the formation.

3. Apparatus for coring a well from a floating platform comprislng:

(a) a string of drill pipe including an upper section and a lower section;

(b) means between said upper and lower sections for permitting vertical movement of said upper section relative to said lower section;

(c) means for anchoring said lower section against vertical movement While permitting rotation of said lower section; and

(d) a hydraulically extensible coring tool mounted on the lower end of said drill string.

4. Apparatus as defined by claim 3 wherein said means for permitting vertical movement is a slip joint.

5. Apparatus as defined by claim 3 wherein said anchoring means is a marine swivel.

6. Apparatus as defined by claim 5 wherein said marine swivel further comprises:

(a) a substantially cylindrical, hollow housing;

(b) a substantially cylindrical, hollow outer mandrel having a cylindrical shoulder on the upper end thereof supportably mounted within the housing and I0- tatable relative thereto;

(0) a cylindrical, hollow inner mandrel slidably disposed within said onter mandrel and having at least one port therethrough opposite the outer mandrel; and

(d) a hydraulically extensible anchor shoe disposed within each of said ports and resiliently sealed thereto.

References Cited UNITED STATES PATENTS 2,927,775 3/ 1960 Hildebrandt 175226 2,929,610 3/1960 Stratton 175-7 X 3,092,191 6/1963 Mori 175-226 3,301,324 1/1967 Smith 166-.5 3,376,927 4/1968 Brown 16655.8 X

JAMES A. LEPPINK, Primary Examiner R. E. FAVREAU, Assistant Examiner US Cl. X.R. l-230 

